1. Field of the Invention
This invention relates to an imaging apparatus and, more particularly, is suitably applied to a case of imaging blood vessel tissues existing inside a body, for example.
2. Description of the Related Art
As a target of biometrics identification, a unique body maker such as irises or fingerprints of a finger or a palm is used.
Recently, a formation pattern of blood vessel tissues existing inside a body is targeted as one of such body markers. An imaging apparatus for imaging a formation pattern of blood vessels has been proposed with using such a feature that light (near-infrared light) of near-infrared light bandwidth is specifically absorbed in deoxygenization hemoglobin (venous blood) or oxygenation hemoglobin (arterial blood) in blood vessels (for example, refer to “Weekly Bio” 49th edition, venous blood matching apparatus, [online], [search on Jan. 24, 2003], Internet <URL:http//www.mackport.co.jp/WEEKLY-BIO/bio49/bio.049.htm>).
FIG. 1 schematically shows a blood vessel imaging apparatus 1. This blood vessel imaging apparatus 1 has laser light sources 2 for emitting near-infrared light. On a light path of the near-infrared light to be emitted from the laser light sources 2, a first filter 3 for allowing specific light of near-infrared light bandwidth out of the near-infrared light to pass therethrough, a second filter 4 for allowing light of near-infrared light bandwidth which is absorbed in hemoglobin in blood vessels, out of the light obtained through the first filter 3, and an imaging element 5 are arranged in order.
In the blood vessel imaging apparatus 1, the light sources 2 irradiate a human finger FG with near-infrared light via the first filter 3, the finger FG being inserted between the first filter 3 and the second filter 4. This near-infrared light is specifically absorbed in intrinsic hemoglobin in the blood vessels of the finger FG, and passes therethrough or is reflected by the other tissues, so that the near-infrared light obtained through the finger FG enters the imaging element 5 via the second filter 4 as blood vessel pattern light representing the formation pattern of the blood vessel tissues.
Then the imaging element 5 performs photoelectric conversion with a plurality of photoelectric conversion elements which are arranged in a reticular pattern so as to correspond to pixels, thereby creating a blood vessel image signal.
However, in an imaging apparatus with both a blood vessel imaging function to image blood vessel tissues of a body as an imaging target, like the above imaging apparatus 1, and a normal imaging function to image a subject such as background or a body, as an imaging target, like a general imaging apparatus, a complicated optical system should be adopted in order to image both near-infrared light which is used for imaging blood vessels and visible light obtained in normal imaging without deteriorating image quality.
One technique to simply solve the above problem is to mechanically arrange a filter for allowing only near-infrared light to pass therethrough in imaging blood vessels, at a prescribed position of an optical system. In this case, such a specially arranged filter increases a circuit scale, which does not meet a portability request. In addition, mechanical switching makes the usage complicated and looses comfort, resulting in deteriorating usability.